Conventional corn processing involves either wet milling or dry milling. Most processed corn has been subjected to the wet milling process. This process includes steeping of the corh to soften the corn kernels for separation of germ and endosperm, followed by grinding and high speed centrifuging to separate corn protein and fiber from corn starch. Corn oil and corn starch are the major products of this process. Corn starch can be further processed to obtain high fructose syrup. By-products of this process are fibers and corn protein. Because of the use of sulfur dioxide and bacterial activity in the steeping step, the by-products are not edible. The by-products are often combined and dried to be used as animal feed. The wet milling process can produce high purity starch, and recover corn oil. The recovery of corn oil can reduce the raw material cost by 25%. However, the operational costs of the wet milling process are high since it requires energy to dehydrate steeping water, and to operate the high speed centrifuges.
Conventional dry corn milling involves tempering the corn with steam to soften the kernel for cracking. Dry corn milling requires a smaller operating cost and a smaller capital investment, but corn oil cannot be totally recovered, and protein cannot be separated from the starch. The major products of this process are corn grits, corn meal and corn flour. Since separation of protein and starch are not necessary when corn is used in fermentation, some of the industry uses this method to prepare corn starch for fermentation. Usually, corn is cracked without tempering, gelantinized and then hydrolyzed by amylases before fermentation. However, separation of corn protein from the hydrolyzed syrup is necessary for the production of high fructose syrup, and purified starch is the preferred raw material. Therefore, wet milling is commonly employed for production of high fructose syrup.
Since the demand for high fructose corn syrup and alcohol increased during the 1970's, it has become desirable to develop a process which is more flexible in the production of final products and, which has smaller operating costs than the conventional processes which, as described above, are either energy intensive or lack flexibility in producing various products. Importantly, any new process should be adaptable to existing corn milling plants. Many different dry milling processes have been developed to produce high fructose syrup, but these processes all ignore the recovery of corn oil, and lack the flexibility to produce granule starch and edible protein. For example, one method employs a dry milling process followed by hydrolysis of starch before separation of corn protein and lipid by filtration. However, such a method encounters problems in the separation of protein, and does not recover corn oil. Further, the process lacks the flexibility to produce high purity granular corn starch, and edible corn protein.
Accordingly, it is a primary object of the present invention to provide an economic process by which corn or other grains are leached with an ethanol solution to yield grain oil while simultaneously dehydrating ethanol. The residue of the leaching step can be processed to yield edible grain protein and grain starch. The starch fraction can be further processed to yield granule starch or hydrolyzed starch to be processed still further to produce alcohol or high fructose syrup.
A further object of the present invention is to provide a process which is easily adaptable to conventional milling operations.